"What I have in my stories is ethics. Ethics and morality are very different cups of tea. I adhere to a very strict rigor of personal ethics and I demand it of those around me as well."
- Harlan Ellison

A living fish which, when placed in your ear, will live there and translate any form of language for you.

Yes, this part of the book was the inspiration for naming the AltaVista website translation feature.

At this point in the novel, Arthur Dent finds himself in a Vogon spacecraft. Their voices are not exactly music to the human ear.

"You'll need to have this fish in your ear."

"I beg your pardon?" asked Arthur.

Ford was holding up a small glass jar which quite clearly had a small yellow fish wriggling around in it…He gasped in terror at what sounded like a man trying to gargle while fighting off a pack of wolves.

Once he had the Babel Fish in his ear, Arthur understood perfectly. The Babel Fish lives on brainwave radiation from every source but its host. It then excretes enegry in the form of exactly the correct brainwaves needed by its host to understand what was just said.

The Babel fish is small, yellow and leechlike, and probably the oddest thing in the Universe. It feeds on brainwave energy received not from its own carrier but from those around it. It absorbs all unconscious mental frequencies from this brainwave energy to nourish itself with. It then excretes into the mind of its carrier a telepathic matrix formed by combining the conscious thought frequencies with nerve signals picked up from the speech centres of the brain which has supplied them. The practical upshot of all this is that if you stick a Babel fish in your ear you can instantly understand anything said to you in any form of language. The speech patterns you actually hear decode the brainwave matrix which has been fed into your mind by your Babel fish.

The Babel Fish reverses the problem defined by its namesake; the original Tower of Babel (according to the Bible) inspired the Deity to confuse human beings by making them unable to understand each other.